Embodiments of the present invention relate to a liquid crystal display device.
Liquid crystal display devices are now being widely used due to their merits of thin thickness and light weight as compared with existing Cathode Ray Tube (CRT) display devices. As shown in FIG. 1, a conventional liquid crystal display device includes a backlight module 10 and a display panel 20. Further, the display panel 20 includes an array substrate 21, a color filter (CF) substrate 23 and a liquid crystal layer 25 filled between the two substrates. The liquid crystal display device is a passive display device, and in order to display pictures, the additional backlight module 10 is provided. On the array substrate 21, there are provided pixel structures (not shown), and in order to display color images, a color filter layer 26 that includes color filters of red (R), green (G) and blue (B) is provided on the color filter substrate 23 in correspondence with each of the pixel structures.
Because the image display needs linearly polarized light, on a light entering face (a face facing the backlight module 100) and a light exiting face (a face of the color filter substrate 23 away from the array substrate 21) of the traditional display panel 20, there are arranged a lower polarizing plate 22 and an upper polarizing plate 24, respectively. Polarization direction and exit amount of light that exits from the backlight module 10 is controlled by the two polarizing plates and the liquid crystal layer 25. Further, light that is transmitted by the lower polarizing plate 22 and the liquid crystal layer 25 will be transmitted by the upper polarizing plate 24 later after they pass through the color filter layer 26, so that the light is fully blocked or transmitted by the upper polarizing plate 24. Thereby, the display panel appears to be a dark state or a bright state. However, before the light is incident to the upper polarizing plate 24, a part of it is scattered upon passing through the liquid crystal layer 25 and the color filter layer 26, so that blocking of the incident light may not be achieved by the upper polarizing plate 202 or the incident light may not be transmitted by the upper polarizing plate 202. Thus, the dark state or the bright state cannot be realized favorably, and accordingly, contrast of the display panel is reduced dramatically. This is more serious especially for IPS and FFS mode display devices in which transverse electric fields are used for control of liquid crystals. To solve this problem, there are methods that properties of a liquid crystal material or size and morphology of pigment particles of color filters are changed, surface treatment is performed on pigment particles of color filters, and so on. However, with respect to each method, it is impossible that the problem of light scattering is avoided radically and then contrast of liquid crystal display devices is raised.
In addition, a color filter allows passage of light with a certain wavelength, and color filters of R, G, and B allow passage of lights with R, G and B wavelengths in an incident white light from the backlight module 10, respectively, namely, only ⅓ of the white light is used. Thus, light loss is large.